Recent reports reveal that helically cut femoral artery strips from renal hypertensive rats usually exhibit spontaneous rhythmic contractions, whereas strips from normal rats do so infrequently. Furthermore, the aortae of hypertensive animals are stiffer and more viscous than those of normal animals. This proposed research is designed to provide observational evidence that will answer the following questions: (1) Is it the viscoelastic or the contractile properties of arterial walls that are first altered during the onset of renal hypertension? (2) Do the viscoelastic and contractile properties of arterial walls return to normal during and/or after hypertension reversal? (3) Do helically cut venous strips from renal hypertensive rats exhibit alterations in their viscoelastic and contractile properties during the onset, duration, and reversal of renal hypertension? These studies use albino rats made hypertensive by unilateral nephrectomy and renal artery clamping. Hypertension is reversed by removing or loosening the renal artery clamp. The following variables are being observed: (1) Young's modulus, (2) viscosity, (3) spontaneous rhythmicity, (4) threshold dosage for norepinephrine, (5) norepinephrine dose-response curves at different resting lengths, (6) effects of altered ion concentrations in the physiological salt solution, (7) histological changes.